could lighten
Regular verb: lighten - lightened- lightened

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could lighten
you could lighten
he could lighten
we could lighten
you could lighten
they could lighten 	I could be lightening
you could be lightening
he could be lightening
we could be lightening
you could be lightening
they could be lightening	I could have lightened
you could have lightened
he could have lightened
we could have lightened
you could have lightened
they could have lightened	I could have been lightening
you could have been lightening
he could have been lightening
we could have been lightening
you could have been lightening
they could have been lightening	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could not lighten
you could not lighten
he could not lighten
we could not lighten
you could not lighten
they could not lighten 	I could not be lightening
you could not be lightening
he could not be lightening
we could not be lightening
you could not be lightening
they could not be lightening	I could not have lightened
you could not have lightened
he could not have lightened
we could not have lightened
you could not have lightened
they could not have lightened	I could not have been lightening
you could not have been lightening
he could not have been lightening
we could not have been lightening
you could not have been lightening
they could not have been lightening	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I lighten?
could you lighten?
could he lighten?
could we lighten?
could you lighten?
could they lighten? 	could I be lightening?
could you be lightening?
could he be lightening?
could we be lightening?
could you be lightening?
could they be lightening? 	could I have lightened?
could you have lightened?
could he have lightened?
could we have lightened?
could you have lightened?
could they have lightened? 	could I have been lightening?
could you have been lightening?
could he have been lightening?
could we have been lightening?
could you have been lightening?
could they have been lightening? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I not lighten?
could you not lighten?
could he not lighten?
could we not lighten?
could you not lighten?
could they not lighten? 	could I not be lightening?
could you not be lightening?
could he not be lightening?
could we not be lightening?
could you not be lightening?
could they not be lightening? 	could I not have lightened?
could you not have lightened?
could he not have lightened?
could we not have lightened?
could you not have lightened?
could they not have lightened? 	could I not have been lightening?
could you not have been lightening?
could he not have been lightening?
could we not have been lightening?
could you not have been lightening?
could they not have been lightening?